A guide to timber frame extensions

If you're considering a timber frame extension or would like to learn more about what timber frame extensions are, this guide will explain it all - from planning permission and costs through to the ins and outs of the build process.



As well as providing your home with additional space and adding value to the property, there are also a host of other benefits to choosing a timber frame extension.


During construction, a timber frame extension allows you to achieve the weathertight stage in a matter of days rather than weeks, which means the builders will not only spend less time on site during its construction, but it's also less dependent on fair weather conditions - this is great news as the levels of disruption are greatly reduced.


Once a timber frame extension is constructed, it offers fantastic levels of thermal performance and airtightness, which makes it the perfect build for projects that put excellent sustainability as a high priority.


If you decide to take the route of opting for a timber frame extension, you'll want to consider a number of things, including how the frame is manufactured, which choice of exterior finish will be most suitable for your property, what sort of planning permission might be required and what can actually be achieved within your budget.


Is a timber frame extension cheaper than other traditional methods?


In most cases a timber frame extension will be cheaper than a traditionally-built extension. The main reason for this is the simple fact that there are typically fewer labour hours involved with the construction process.


It's also much easier for builders to predict an accurate estimated build-time as construction is less dependent on weather conditions - something that can often push extension builds back many weeks, particularly during the winter months, when other traditional methods are used.


Gaining finance for a timber frame extension


If you plan to remortgage in order to help finance a timber frame extension be sure to always ask the lender what external finishes they deem acceptable. Some lenders are more conservative than others on what external finish they will accept, so checking beforehand will ensure that you choose a lender who is happy help finance the proposed works.


Also, as with any large home improvement or house extension project, you'll want to make sure that the work you plan to do to your home will be adding more value to the property than it costs to carry out the work.


This new thermally insulated timber extension improves energy efficiency while boosting the exterior aesthetics of this 1960s detached home.


Do I need planning permission to build a timber frame extension?


Fortunately, planning permission is usually not necessary to build a timber frame extension. If your extension plans meet certain criteria in terms of its overall size and position, then it may be possible for you to extend the property under Permitted Development Rights (PD). However, if your extension plans involve building something that's outside the scope of PD, then you will need to obtain planning permission beforehand.


It's important to always double check with your local authority before undertaking any building work to your home, especially if it's a listed property, or located in a conservation area or Area of Outstanding Natural Beauty. Any reputable building firm will also check on your behalf before starting any work should you have any worries or doubts.


(MORE: Useful tips to help you choose a reputable builder)


Does a timber frame extension get built on site?


Most extensions that are built using timber frame are 'stick build', which means timber frame panels are made up on site by the professional joiners as opposed to being manufactured in a factory environment. A structural engineer would carefully design the timber frame and prepare a specification of the size and grade of timbers to be used for the frame, lintels, cripple studs and so on, along with a nailing schedule.


Your building firm would take delivery of the timbers that are required, and thanks to the timbers being loose upon delivery they can be easily carried through tight or restricted access areas to the location where the panels are to be erected.


Some positives to a timber frame extension include quick assembly, energy efficiency, cost-effective and design possibilities that are endless.


The timber frame panels will then be made up on site by the joiner to the specifications set out from the structural engineer. The existing structure will be exposed by this point, which means accurate dimensions can be taken so that the timber panels can be manufactured to suit.

Design features that include large expanses of glazing may require a steel or glulam portal frame to be installed, but this aspect will have been advised by the structural engineer during the planning process. This can be created off-site, delivered in separate sections and then bolted together on site at the start of the construction phase.


It's important to note that if any part of the extension is below ground level then timber frame construction would not be suitable for that particular part of the build. In this instance, a different method of extension build can be used in combination with the timber frame.


Can factory-manufactured timber frame be used for an extension?


Many manufacturers aren't keen to supply a quote for extension projects because they tend to require a lot of technical input when compared to a new build. Before an extension is built, extremely accurate site dimensions are required so that floor levels, eaves, roofs and the like can all line up perfectly with the rest of the existing property.


It is often extremely difficult, or perhaps at times impossible, for these accurate manufacturing dimensions to be recorded until all elements of the existing property can be exposed. Only once this has happened is it possible to establish exactly how the property was originally constructed. This can mean considerable delays before the build even begins as the majority of manufacturers will have a lead-in time of 6-8 weeks from obtaining all of the relevant information they require beforehand to the point of delivery.


If a site is very restrictive, which can often be the case with a house extension, then this may also discourage a manufacturer from providing a quote. Furthermore, a typical single storey extension of say around 3.6 x 4.8m will only require a part load, which makes the transportation costs uneconomical when compared with a 'stick build'.


This timber frame dining extension marries the inside with the outside beautifully thanks to large expanses of glazing and the airy rustic vibe created from the timber interior.


Which exterior finishes work on a timber frame extension?


The beauty of a timber frame extension is the multitude of external finishes that are available for you to choose from.


A variety of the materials that can be chosen include:


  • Facing brick

  • Natural stone

  • Reconstituted stone

  • Timber

  • Rendered brickwork/blockwork

  • Metal cladding

  • Fibre cement cladding

  • Brick slips

  • Render board system


However, if the timber frame extension is being built on a boundary the external finish must be a non-combustible material and offer a minimum of one hour's fire resistance to satisfy current Building Regulations.


The Building Regulations are extremely detailed and can be found in full on the Housing, local and community Government website.


Tips to help you extend with timber frame


  • Choose a designer and building firm who are experienced with timber frame extensions

  • Obtain a detailed quote and ensure you understand every aspect of it - ask if necessary

  • Make sure you have a contingency budget in place to account for unforeseen circumstances

  • Budget for external works such as paving, decking and landscaping


Combining a timber frame extension with other traditional or contemporary exterior finishes can create a striking juxtaposed result, as demonstrated with this rear house extension.


Factoring in the all-important movement joints


No matter which construction method is used, when an extension is attached to an existing building it's vital that a movement joint is formed to help accommodate any shrinkage, thermal and moisture movement.


It's very likely that the extension will be built as a different construction to that of the existing building, which means it will expand and contract at a different rate to the existing building. This is why a movement joint is essential.


A stainless steel channel tie system is usually formed to create movement joints which provide lateral restraint while also allowing for both horizontal and vertical movement. The gap which is formed between the two structures is filled with a flexible sealant to ensure that it's made weathertight - and you'll be pleased to know that these sealants are available in a range of colours to not look out of place on your property.


If you'd like to learn more about home extensions, or would like to discuss any of the other home improvement and building services that we offer here at RGB Construction, then don't hesitate to get in touch with us. You can call on 07946452571, e-mail enquiries@rgbconstruction.info or fill in the online contact form.


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